Understanding The Follicular Phase Of The Menstrual Cycle
During the follicular phase, the brain signals the release of the FSH, which releases fluid-filled sacs called follicles, containing immature eggs. When estrogen levels increase, the blood vessel supply also increases, and the inside lining of the uterus starts to thicken.
Approximately 11 to 20 follicles develop during this follicular phase. During this development, one oocyte will become more dominant than the rest, and will eventually be released—that is precisely when someone can become pregnant.
There’s also an increase in the luteinizing hormone (LH), which slightly peaks at the end of the follicular phase. This occurs directly before ovulation, and is what stimulates the release of the mature egg.